Diacetylenes are typically colorless and undergo addition polymerization, either thermally or by actinic radiation. As the polymerization proceeds, these compounds undergo a contrasting color change to blue or purple. When exposed to external stimuli such as heat, physical stress or a change of solvents or counterions, polydiacetylenes exhibit a further color changes produced by distortion of the planar backbone conformation. Polydiacetylene assemblies are known to change color from blue to red with an increase in temperature or changes in pH due to conformational changes in the conjugated backbone as described in Mino, et al., Langmuir, Vol. 8, p. 594, 1992; Chance, et al., Journal of Chemistry and Physics, Vol. 71, 206, 1979; Shibutag, Thin Solid Films, Vol. 179, p. 433, 1989; Kaneko, et al., Thin Solid Films, Vol. 210, 548, 1992; and U.S. Pat. No. 5,672,465. Utilization of this class of compounds is known for use as biochromic indicators as discussed in U.S. Pat. No. 5,622,872 and publication WO 02/00920.
Proposed applications of polydiacetylenes for detection of analytes are discussed in U.S. Pat. Nos. 6,395,561 B1; 6,306,598 B1; 6,277,652; 6,183,772; 6,080,423 and publication WO 01/71317. In particular, attempts have been made to construct biosensors with receptors that react specifically with pathogenic bacteria, viruses, toxins and the like incorporated into polydiacetylene membranes, and the color change (blue to red) is induced when the receptors bind to their specific analytes (pathogenic bacteria, viruses, toxins, etc.) Such methods require that the binding structure of the receptor and analyte be known, and the receptor identified. Synthesis of both the receptors and the polydiacetylene membranes can be complicated and difficult. The polydiacetylene membranes can exhibit insufficient color change upon binding with an analyte, requiring other substances for promoting the structural change or enhancing analytical equipment to observe the color change.